Perfluoroketovinyl ethers and copolymers therefrom

ABSTRACT

Perfluoroketovinyl ether of the formula (as in claim 1) wherein n is an integer 1 to 4; copolymers of such ether and a fluorinated monomer, such as tetrafluoroethylene; ion-exchange resins of such copolymers; and ion-exchange membranes of such resins.

CROSS-REFERENCE TO RELATED APPLICATION

This is a division of application Ser. No. 279,024 filed June 30, 1981and issued May 24, 1983 as U.S. Pat. No. 4,385,187.

DESCRIPTION

1. Technical Field

This invention relates to perfluoroketovinyl ethers and toperfluorinated copolymers prepared from such ethers.

2. Background

U.S. Pat. No. 4,138,426 discloses perfluorovinyl ether carboxylates ofthe formula ##STR1## wherein Y is --CO₂ R, --CO₂ H, --CO₂ M or --CN, Ris C₁ to 6 alkyl, M is alkali metal, ammonium or quaternary ammonium andp is an integer 1 to 5.

Japanese Publication J5 5015-410 discloses the thermal decomposition, at230°-400° C., of metal salts of the formula ##STR2## wherein M is alkalimetal, n is 0 or an integer 1 to 3, m is 0 or an integer 1 to 4 andn+m≠0. The products are divinyl ethers of the formula ##STR3##

R. E. Banks, "Fluorocarbons and Their Derivatives," Elsevier (1970),page 22, discloses the solventless pyrolysis of perfluorovinylcarboxylic acid salts to perfluorodiolefins at 100°-450° C. and 0.01 mmHg (1.3 Pa), for example, CF₂ ═CFCF₂ CF₂ CO₂ Na to CF₂ ═CFCF═CF₂, CO₂and NaF.

It is known that in the pyrolysis of acyl fluorides ##STR4## or thecorresponding carboxylic acid salts ##STR5## to vinyl ethers(--OCF═CF₂), CO₂ and NaF, use of solvents such as tetraglyme is optionalbut may facilitate pyrolysis at lower temperatures. U.S. Pat. No.3,114,778 discloses the pyrolysis of perfluorodicarboxylic acid salts todivinyl ethers, for example, ##STR6## to CF₂ ═CFO(CF₂)_(n) OCF═CF₂, CO₂and NaF, without solvent, at 170°-250° C. or, using solvent, attemperatures as low as 100° C. U.S. Pat. No. 3,326,984 discloses thepyrolysis of an unsymmetrical perfluorodicarboxylic acid salt of theformula ##STR7## to the divinyl ether CF₂ ═CFOCF═CF₂, without solvent,at 200°-300° C., or in an inert polar solvent such as tetraglyme, at100°-200° C. In neither patent are different products or differentproduct distributions, in the presence or absence of solvent, disclosed.

Hudlicky, "Chemistry of Organic Fluorine Compounds," MacMillan (1962),page 271, discloses the pyrolysis of salts of perfluoromonocarboxylicacids, both in the presence and absence of ethylene glycol as thesolvent. For example, potassium perfluoropentanoate yields CF₃CF═CF--CF₂ and CF₃ CF₂ CF═CF₂ at 165°-200° C., but yields CF₃ CF₂ CF₂CF² H at 170°-190° C. in the presence of ethylene glycol.

U.S. Pat. No. 3,847,978 discloses perfluoroketoacyl fluorides of theformula ##STR8## wherein n is 1 to 50 X is COF or CO₂ H. No ketovinylethers are disclosed.

DISCLOSURE OF INVENTION

For further comprehension of the invention, and of the objects andadvantages thereof, reference may be made to the following descriptionand to the appended claims in which the various novel features of theinvention are more particularly set forth.

This invention resides in the perfluoroketovinyl ether of the formula##STR9## wherein n is an integer of 1 to 4, and in copolymers of theether 1 and a fluorinated vinyl monomer such as tetrafluoroethylene,chlorotrifluoroethylene, trifluoroethylene, perfluoroalkylvinyl etherwherein the perfluoroalkyl group contains 1 to 4 carbon atoms,vinylidene fluoride, or combinations of these vinyl monomers. Theinvention also resides in molded objects of such copolymers, forexample, ion-exchange membranes. The invention further resides in aprocess for preparing the ether 1 from the known perfluorovinyl ethercarboxylic acid salt of the formula ##STR10## wherein m is an integer 2to 5 and M is an alkali or alkaline earth metal.

The ketovinyl ether 1 is prepared by heating the salt of formula 2 in anaprotic ether solvent, such as a glyme (i.e., mono-, di-, tri- ortetraethyleneglycol dimethyl ether), preferably tetraglyme, at atemperature of 130° to 300° C., preferably 170° to 230° C. Preferably,the solvent should be higher boiling than the reaction products. It isessential to the preparation of the ketovinyl ether 1 that thecarboxylic acid salt 2 by pyrolyzed in an appropriate solvent. If salt 2is pyrolized in the absence of solvent, the ketovinyl ether is formed invery minor amounts, if at all.

It is important that the solvent and the salt 2 be moisture-free. Thepresence of water or other substances which can yield a proton duringpyrolysis lowers the yield of the desired ether 1 by producing thehydrogen-capped by-product of the formula ##STR11## wherein n is aninteger 1 to 4. The formation of this by-product is demonstrated inExamples 1 and 4 and in Experiment 1.

Various methods of drying the salt 2 can be used, including evaporationof water, azotropic distillation of water with toluene andneutralization in methanol solution followed by evaporation of methanol.In all these cases final drying in a vacuum oven is required to ensurecomplete removal of water or methanol. Neutralization in methanol ispreferred because less foam is generated in the drying process, and thelower boiling point and lower heat of vaporization of methanol relativeto water increases the drying rate. Solvents for the pyrolysis are driedby standard methods for drying organic liquids; distillation from sodiumhydride is convenient.

Preferred salts are of formula 2 wherein M is Na. Other alkali metal oralkaline earth metal salts can be employed, but they are generally moredifficult to dry adequately. Example 4 illustrates the use of a calciumsalt. An oven temperature of 140° C. was required to dry the calciumsalt, in contrast to 100° C. typically used to dry the sodium andlithium salts. Even at this high temperature in Example 4, the calciumsalt still contained about 0.5 mole of water per mole of salt. Thisundoubtedly contributed to the comparatively low yield of the desiredketovinyl ether 1 and the larger amount of hydrogen-capped by-product.The lithium salt (Example 5) is also more difficult to dry than thesodium salt and is more hygroscopic. Sodium salts are preferred overpotassium and other alkali metal salts, also, for economic reasons.

As already shown in formula 2 for the perfluorovinyl ether carboxylicacid salt, m is at least 2. As shown in Experiment 1, a pyrolysis of asalt of the formula wherein m is 1 yields as the principal product anacyl fluoride. Pyrolysis of a salt of the formula wherein m is 0 yieldsa divinyl ether, as disclosed in the art.

Pressure is not a critical variable for the pyrolysis of the salt 2. Apressure above or below atmospheric pressure can be employed.Atmospheric or subatmospheric pressure is preferred, however, because ofthe comparative ease of recovering the distillable reaction products.

Use of a catalyst in the pyrolysis of the salt 2 is neither required nordesirable.

The perfluoroketovinyl ether 1 can be copolymerized with a fluorinatedvinyl monomer such as tetrafluoroethylene, chlorotrifluoroethylene,trifluoroethylene, perfluoroalkylvinyl ether wherein the perfluoroalkylgroup contains 1 to 4 carbon atoms, vinylidene fluoride, or combinationsof these vinyl monomers. Well-known, free radical-initiated additioncopolymerization methods can be employed.

Copolymers prepared from the ketovinyl ether of formula 1 and a vinylmonomer contain repeat units of the formula ##STR12## wherein X is F orH; Z is F, H, Cl or OR wherein R is perfluoroalkyl of 1 to 4 carbonatoms; n is an integer 1 to 4; and q is about 3 to about 200, preferablyabout 6 to about 50. The copolymers are moldable, as demonstrated by thepreparation of films therefrom by hot-pressing. The copolymers can behydrolyzed by treatment with either dilute (for example, 10 weight %)aqueous mineral acid or aqueous alkali. The ion-exchange properties ofthe copolymer can be demonstrated by hydrolyzing the copolymer in 10%aqueous sulfuric acid to convert the carbonyl group to a gem diol, thenimmersing the washed, acid-hydrolyzed copolymer in 10% aqueous sodiumchloride solution containing an excess of sodium hydroxide, andback-titrating the residual alkali.

The copolymers having repeat units of formula 4, or their hydrolysates,can be converted to carboxyl-functional copolymers by treatment withstrong alkali (haloform reaction). The resultant copolymers have repeatunits of formula 4 except that the chain end group is CO₂ M instead ofCOCF₃, M being an appropriate cation, and they are useful asion-exchange resins and as ion-exchange membranes in chloralkalielectrolysis cells. A membrane of the copolymer having repeat units offormula 4 can be used in such a cell because the copolymer is rapidlyhydrolyzed, then subsequently converted to the carboxylate (--CO₂ M)form in situ in the strongly alkaline medium of the cell. Bothhydrolysate and carboxylate forms have ion-exchange properties asindicated above. Preferably, the membranes are hydrolyzed prior to celluse.

The copolymers are dyeable with dyes containing an NH or OH moiety andthey are crosslinkable with compounds containing a plurality of NHand/or OH moieties by virtue of known chemistry of the perfluoroketogroup. The hydrolyzed copolymers are similarly dyeable, and they can becrosslinked by reaction with isocyanates.

In the following examples which illustrate the invention, parts andpercentages are by weight unless otherwise indicated.

EXAMPLE 1

This example describes the preparation of a perfluoroketovinyl ether offormula 1 from the sodium salt of formula 2.

100 Grams (0.170 mole) of methylperfluoro-5,8-dimethyl-4,7,10-trioxa-11-dodecanoate was placed in aflask with 100 ml of water. 6.9 Grams (0.173 mole) of sodium hydroxidewas dissolved in a small amount of water and added dropwise, withstirring, to the flask. The reaction mixture became a slurry. Whenaddition of the sodium hydroxide was completed, the water was evaporatedon a steam bath under a stream of nitrogen. The sodium salt obtained wasthen dried in a vacuum oven at 120° C.

The salt (50 g) thus obtained was added to a dry 250 ml flask containinga magnetic stirring bar and a side arm with a thermometer. The flask wasflushed with nitrogen and connected to a distillation head; 100 ml oftetraglyme was added to the flask. The contents of the flask were heatedstrongly. By the time the temperature of the reaction mixture reached160° C., the salt had dissolved and gas evolution was noted. Heating wascontinued and the temperature rose to 200° C. Gas evolution increasedwith the temperature and product began to distill. Heating was continueduntil distillation stopped. A total of 22 g of a product mixture wascollected. Analysis of the product by gas chromatography showed thepresence of two components accounting for 65% and 35% of the mixture,respectively. The components of the mixture were separated by fractionaldistillation and were identified by their fluorine nuclear magneticresonance spectra and by their infrared spectra. The major product wasperfluoro-5-methyl-8-oxo-3,6-dioxa-1-nonene and the minor product was11H-perfluoro-5,8-dimethyl-3,6,9-trioxa-1-undecene.

EXAMPLE 2

This example describes the preparation of a perfluoroketovinyl ether offormula 1 from the sodium salt of formula 2.

52 Grams (0.0885 mole) of the starting ester used in Example 1 wasplaced in a flask with 50 ml of methanol containing 3.54 g (0.0885 mole)of sodium hydroxide. The mixture was warmed with stirring until the pHwas 6-7 as indicated by test paper. Most of the methanol was removed ina rotary evaporator to yield a viscous oil. The remaining methanol wasremoved on a steam bath under a stream of nitrogen. The white solidsodium salt which was obtained, after drying in a vacuum oven at 100°C., weighed 47.2 g. It was placed in a flask along with 100 ml oftetraglyme and heated to 200°-210° C. The productperfluoro-5-methyl-8-oxo-3,6-dioxa-1-nonene was distilled from thereaction mixture as it formed; yield, 13.8 g.

EXAMPLE 13

This example describes the preparation of a perfluoroketovinyl ether offormula 1 from the sodium salt of formula 2.

Sodiumperfluoro-5,8,11,14-tetramethyl-4,7,10,13,16-pentaoxa-17-octadecanoatewas prepared by adding 12.5 g of the corresponding methyl ester and 10ml of water containing 0.55 g of sodium hydroxide to a flask containing50 ml of water. The contents of the flask was warmed gently and stirreduntil a viscous solution was formed of neutral pH. The water wasevaporated and the salt remaining was dried at 110° C. in a vacuum oven.

The dry salt was pyrolyzed at 200°-210° C. in 50 ml of tetraglymedistilled from sodium hydride. When the pyrolysis was completed, thepressure in the apparatus was gradually lowered by means of a vacuumpump to 155 mm of Hg (20.6 kPa). Product distilled at 145°-155° C. wascollected; 5.2 g. Gas chromatographic analysis showed it to be amixture, with the major product accounting for 70% of the mixture. Themajor product which was isolated by fractional distillation andidentified from its infrared and fluorine nuclear magnetic resonancespectra wasperfluoro-5,8,11-trimethyl-14-oxo-3,6,9,12-tetraoxa-1-pentadecane.

EXAMPLE 4

This example describes the preparation of a perfluoroketovinyl ether offormula 1 from the calcium salt of formula 2.

200 Grams (0.340 mole) of the starting ester used in Example 1 was mixedwith 15 g (0.375 mole) of sodium hydroxide dissolved in 500 ml water.The mixture was stirred until it was neutral; then, 38 ml ofconcentrated hydrochloric acid was added. The reaction mixture separatedinto two layers. The bottom layer was removed and the top layer wasextracted with three 200 ml portions of diethyl ether. The etherextracts were combined with the bottom layer from above and dried overmagnesium sulfate. The ether was evaporated to yield 179.7 g ofperfluoro-5,8-dimethyl-4,7,10-trioxa-11-dodecanoic acid.

50 Grams (0.0871 mole) of the acid and 3.2 g (0.0432 mole) of calciumhydroxide were shaken with 300 ml of water until a gelatinousprecipitate formed. The precipitate was isolated and taken up inmethanol to yield a turbid solution which was filtered to yield a clearsolution of neutral pH. The methanol was evaporated to yield the whitesolid calcium salt which was dried at 110° C. in a vacuum oven for 24 hto constant weight. Additional water was driven off by drying another 23h at 140° C. A portion (33 g) of the calcium salt was pyrolyzed intetraglyme freshly distilled from sodium hydride. Analysis of theproduct which was collected by distillation, 8.8 g, showed that 19% ofit was perfluoro-5-methyl-8-oxo-3,6-dioxa-1-nonene and 38% was11H-perfluoro-5,8-dimethyl-3,6,9-trioxa-1-undecene.

EXAMPLE 5

This example describes the preparation of a perfluoroketovinyl ether offormula 1 from the lithium salt of formula 2.

1.3 Grams (0.043 mole) of lithium oxide was dissolved in 300 ml ofwater. 50 Grams (0.087 mole) ofperfluoro-5,8-dimethyl-4,7,10-trioxa-11-dodecenoic acid prepared as inExample 4 was dissolved in 150 ml of methanol and mixed with the lithiumoxide solution. The pH of the mixture was neutral. The solvents wereevaporated and the salt was dried 6 days in a vacuum oven at 110° C. At110° C. the dry salt is a plastic mass which hardens to a hygroscopicglass at room temperature. 25.9 Grams of the lithium salt was placed ina flask and pyrolyzed in tetraglyme as described in Example 1. Productdistilled to yield 9.0 g of material which was analyzed and shown tocontain 76% of the ketovinyl etherperfluoro-5-methyl-8-oxo-3,6-dioxa-1-nonene.

EXAMPLE 6

This example describes the preparation of a copolymer oftetrafluoroethylene and the perfluoroketovinyl ether of formula 1. Italso demonstrates the utility of the copolymers of the invention asion-exchange resins.

A 500 ml pyrex pressure bottle containing 10.0 g ofperfluoro-5-methyl-8-oxo-3,6-dioxa-1-nonene, 11 ml of CFCl₂ CF₂ Cl and50 mg of perfluoropropionyl peroxide was placed on a Parr pressurereaction apparatus. The apparatus was pressured to 60 psig (414 kPa)with tetrafluoroethylene and a constant pressure of 60 psig (414 kPa)was maintained by means of a regulator. The polymerization was allowedto proceed for 3 h. The apparatus was vented and 1.84 g of polymer wasisolated by evaporating solvent and unused monomers. A sample of thepolymer was hot pressed into a film. An infrared spectrum of the filmshowed a carbonyl band at 1810 cm⁻¹, characteristic of the keto group. Asample of the film was heated in 10% sulfuric acid on a steam bath for 2h and then washed neutral. The sample was soaked in 10% aqueous sodiumchloride containing 1.011 meq of sodium hydroxide. Titration of excesssodium hydroxide with standard acid showed the equivalent weight of thepolymer to be 1401. Thus, q in the aforesaid formula 4 is approximately9.9.

EXAMPLE 7

This example describes the preparation of a copolymer oftetrafluoroethylene and the perfluoroketovinyl ether of formula 1.

A 75 cc pressure bomb was charged with a weighed amount ofperfluoro-5-methyl-8-oxo-3,6-dioxa-1-nonene and 10 ml of CFCl₂ CF₂ Clcontaining perfluoropropionyl peroxide. The bomb was closed and cooledin dry ice/acetone. The bomb was then evacuated and repressurized withnitrogen. This nitrogen flush procedure was repeated three times andthen 10.0 g of tetrafluoroethylene was charged to the bomb. The bomb wasplaced on a shaker and warmed to 60° C. for 3 h. After cooling to roomtemperature the bomb was vented and opened. The polymer, swollen withsolvent, was removed and dried. Equivalent weights were determined asdescribed in Example 6. Experimental data are presented below for tworuns.

    ______________________________________                                             Perfluoro- perfluoro-5-                                                       propionyl  methyl-8-oxo-  Pressure                                                                             Pressure                                Run  peroxide (mg)                                                                            3,6-dioxa-1-nonene (g)                                                                       (psig) (kPa)                                   ______________________________________                                        A     5         10.0           125-105                                                                              862-724                                 B    26         40.0           178-110                                                                              1228-758                                ______________________________________                                             Reaction                Equivalent                                       Run  Time (h)  Copolymer (g) Weight   g                                       ______________________________________                                        A    3          1.7          >12,000  >115                                    B    1         11.9            1,915    15                                    ______________________________________                                    

EXPERIMENT 1

This experiment shows the different result that is obtained when thestarting salt contains only one hexafluoropropylene oxide unit, that is,when m is formula 2 is one (outside the invention).

67 Grams of sodium perfluoro-5-methyl-4,7-dioxa-8-nonenoate was placedin a flask and 100 ml of tetraglyme was vacuum distilled from sodiumhydride into the flask. The flask was connected in sequence to adistillation head and a trap cooled by dry ice/acetone. The mixture washeated as described in Example 1. The first evolution of gas was notedat 149° C., with vigorous evolution occurring at 175° C. Productdistilled from the reaction mixture. A total of 21.2 g was collected inthe receiver of the distillation head. This product was shown to beperfluoro-5-methyl-4,7-dioxa-8-nonenoyl fluoride by its fluorine nuclearmagnetic resonance spectrum.

The cold trap contained a small amount of material. Chlorine wascondensed into the cold trap so that a higher boiling, more easilyhandleable mixture of products was obtained. The mixture, which totaled2.4 g after chlorination, was separated by gas chromatography and thecomponents issuing from the chromatograph were analyzed by massspectrometry. The components included tetrafluoroethylene,perfluoro-5-oxo-3-oxahexene and its chlorinated derivative1,2-dichloro-1,1,2,4,4,6,6,6 -octafluoro-5-oxo-3-oxahexane,perfluoro-5-methyl-4,7-dioxa-8-nonenoyl fluoride and8H-perfluoro-5-methyl-3,6-dioxaoctene.

BEST MODE FOR CARRYING OUT THE INVENTION

The best modes presently contemplated for the invention are demonstratedin Examples 2 and 3 for the perfluoroketovinyl ether of formula 1, andits preparation, and in Examples 7 for the copolymer prepared from theether 1 and a vinyl monomer.

INDUSTRIAL APPLICABILITY

The perfluoroketovinyl ether 1 is useful as a copolymerizable monomerfrom which fluorinated copolymers useful as molding resins can beprepared. The copolymers, after conversion by hydrolysis or othertreatment, are also water-wettable, dyeable, possess ion-exchangeproperties and are useful in curable fluoroelastomer compositions.

Although the preferred embodiments of the invention have beenillustrated and described above, it is to be understood that there is nointent to limit the invention to the precise constructions hereindisclosed and it is to be further understood that the right is reservedto all changes and modifications coming within the scope of theinvention as defined in the appended claims.

I claim:
 1. Copolymer of the perfluoroketovinyl ether of the formula##STR13## wherein n is an integer 1 to 4 and one or more fluorinatedvinyl monomers.
 2. Copolymer of perfluoroketovinyl ether of the formula##STR14## wherein n is 1 and one or more fluorinated vinyl monomers. 3.Copolymer of claim 1 wherein the fluorinated vinyl monomer istetrafluoroethylene.
 4. Film of the copolymer of claim
 1. 5. Copolymerof claim 1 which has been hydrolyzed in an aqueous medium.